Conventionally, a stent is applied in order to improve a stenosed site or an obstructive site which has occurred inside a living body lumen such as a blood vessel, the bile duct, the trachea, the esophagus, urethra, and the like. The stent is formed with a metal wire and the like, has a cylindrical shape in its entirety, is configured to have multiple side wall openings, and is expandable in a living body lumen.
As a type of the stent, there is a balloon expandable stent, which is mounted on a balloon of a balloon catheter and indwells in a living body lumen by being widened from the inner side by the balloon. In addition, another type of the stent, is a self-expandable stent which is provided with a function of self-expansion conducted by elastic force and indwells in a living body lumen by being released from a sheath or the like in the living body lumen and conducting self-expansion. A stent delivery system is applied in order to deliver the balloon expandable stent or the self-expandable stent to a desired position inside a living body lumen and to indwell the stent therein.
Generally, a stent delivery system having a conventional self-expandable stent includes an inner tube, a stent that is mounted outside the inner tube in the vicinity of a distal end portion thereof, an outer tube that is displaceable in an axial direction outside the inner tube and accommodates the stent in a contracted state, and a grip that is connected to a proximal end portion of the outer tube. In a procedure in which the stent delivery system is applied, the stent is delivered to the inside of a living body lumen in a state of being compressed and contained in an aperture between the inner tube and the outer tube, and the stent is released and indwells in the living body lumen by moving the outer tube in a proximal direction with respect to the inner tube.
In the stent delivery system, a movement mechanism for causing the outer tube to relatively move in the axial direction with respect to the inner tube is further provided in the grip. The movement mechanism has a rotatable operation wheel and a rack member, which is provided with a rack that meshes with a pinion provided in the operation wheel. Then, the proximal end portion of the outer tube is connected to the rack member. When the operation wheel of the aforementioned movement mechanism rotates in a predetermined direction, the rack member moves rearward and the outer tube thereby moves rearward with respect to the inner tube in accordance with a movement thereof. Thus, the stent is released from the outer tube to the inside of a living body lumen. JP-T-2007-504897 discloses a conventional stent delivery system, for example.
Stents can also have a long overall length (for example, equal to or greater than 20 cm) in accordance with a site to be treated. In addition, a plurality of stents can be arranged side by side in an axial direction of an inner tube and the plurality of stents can be released and indwelled in a living body lumen. In order to release a stent having the long overall length or a plurality of stents inside a living body lumen, a movement distance of a rack member in a proximal direction from the initial position needs to be elongated. In a conventional stent delivery system, since the rack member is configured to be moved by one pinion, the rack member requires an overall length corresponding to a necessary movement distance in order to move the rack member rearward as far as the necessary movement distance. Then, since the rack member is arranged so as to extend from the pinion side in a distal direction at the initial position, a grip is required to extend in the distal direction in accordance with the length of the rack member. As a result thereof, there is an occurrence of a problem in that the overall length of the grip is elongated and the tractability thereof during a procedure can deteriorate.